The Cumberland River is a waterway in the southern United States. It is 688 miles (1,107 km) long. Its tributaries are three separate forks that begin in Kentucky, and converge in its Harlan County. Martin's Fork starts in Hensley Settlement on Brush Mountain in Bell County and snakes its way north through the mountains to Baxter. Clover Fork starts on Black Mountain in Holmes Mill, near the Virginia border, and flows west in parallel with Kentucky Route 38 until it reaches Harlan. Clover Fork once flowed through downtown Harlan and merged with Martin's Fork at the intersection of Kentucky Route 38 and US Route 421, until a flood control project in 1992 diverted it through a tunnel under Little Black Mountain, from which it emerges in Baxter and converges with Martin's Fork. Poor Fork begins as a small stream on Pine Mountain in Letcher County near Flat Gap, Virginia. It flows southwest in parallel with Pine Mountain until it merges with the other two forks in Baxter. From there, the wider river continues flowing west through the mountains of Kentucky to Cumberland Falls.